In manufacturing operations using metal strip material processes where continuous milling is performed, there is a need to join the metal strips together without disrupting the quality of the product for the continuous process. The usual method of joining metal strips together is to utilize an arc welding process either prior to or during the milling process. In many cases the strip end welds are eventually cut out of the final product and thus the only requirement for these strip end welds is that they maintain their mechanical integrity during milling of the strip material. However, in other instances the strip end welds become part of the final product, in which event not only are the strip end welds required to maintain mechanical integrity throughout the milling process, but they also must ultimately perform as well as the strip material in the final product.
When an extremely high quality weld is required, a variety of well known steps may be used in preparing the strip end joint for welding which may include using tabs to prevent burn out at the strip edges, cutting the strip ends at supplementary angles so that the weld joint is angled across the finished strip rather than being perpendicular to the strip side edges, and removing excess weld reinforcement to increase fatigue life of the weld joint and to facilitate forming of the strip.
For steel strips that are less than 0.200 inch thick, the common industry practice is to abut the strip ends together. When the strip thickness exceeds 0.200 inch, it becomes increasingly more common to either bevel the edges of the strip ends prior to welding or to leave a slight gap between the strip ends. These procedures facilitate full penetration of the weld through the full cross section of the joint.
If the strip ends are abutted, sufficient weld power must be used to allow the weld arc to completely penetrate the full cross section of the strip end joint. As the arc moves down the joint line, filler material is deposited in the molten pool created by the arc. The molten weld pool consists of the deposited filler metal and diluted parent metal from the strips. As the arc progresses along the joint line, the back of the weld pool cools and begins to solidify. During the solidification process, the strip material contracts and stresses occur that, in some cases, can actually result in cracks in the strip end weld.